1. Field of the Invention
The present invention relates to a laminated electronic component formed by compression bonding and laminating a ceramic substrate and a resin sheet, and a method for producing the same.
2. Description of the Related Art
To achieve miniaturization and high function of radio communication devices such as cellular phones, components installed therein must provide high function in smaller spaces. In order to meet this demand, a laminated electronic component including a ceramic multilayer substrate has been used.
Recently, low temperature co-fired ceramic (LTCC) multilayer substrates have been primarily used as such ceramic multilayer substrates. This is because the LTCC can be fired at a low temperature of up to about 1,000° C., and a low resistance metal, such as silver or copper, can be used as a wiring conductor.
However, since the LTCC often includes a considerable amount of glass in order to decrease the firing temperature, the LTCC is more fragile than pure ceramics. For example, pure alumina has a flexural strength of about 300 MPa, whereas a glass ceramic including alumina and glass with a 50:50 by volume ratio has a flexural strength of about 200 MPa.
Therefore, when a drop test is performed with such a ceramic multilayer substrate mounted on a printed wiring board, a tensile stress is generated at a bonded portion between the ceramic multilayer substrate and the printed wiring board. As a result, cracks are easily produced on the mounting surface of the ceramic multilayer substrate.
Japanese Unexamined Patent Application Publication No. 2003-7367 (Patent Document 1) proposes a combined ceramic component in which a resin layer for shock absorption is provided on the mounting surface of a ceramic multilayer substrate.
When such a combined ceramic component is mass-produced, a method in which a master substrate of a ceramic multilayer substrate is divided to form sub-substrates is generally used. Examples of the method for dividing include dividing by cutting with a dicer and dividing by breaking along a dividing groove.
In order to mass-produce the ceramic multilayer substrate described in Patent Document 1, first, a resin sheet must be bonded on a master substrate of the ceramic multilayer substrate, the resin sheet having approximately the same area as that of the master substrate. A resin sheet including a thermosetting resin, such as an epoxy resin, and an additional inorganic filler composed of, for example, SiO2, is primarily used.
According to a method for bonding the resin sheet, as described in Patent Document 1, a resin sheet including a thermosetting resin in a semi-cured state (in a B-stage state or a prepreg state) is compression bonded on the ceramic multilayer substrate by heating.
However, when a resin sheet having the same area as that of the master substrate is compression bonded, air is often trapped in the interface between the ceramic multilayer substrate and the resin sheet because of the large area. This air is expanded by heat during, for example, the reflow of solder, which causes a problem that the ceramic multilayer substrate is separated from the resin layer.
In addition, when the air is trapped in a conducting portion between the ceramic multilayer substrate and the resin sheet (for example, an interface between an electrode of the ceramic multilayer substrate and a via hole conductor of the resin sheet), conduction failure may be caused.